Germs...so many germs. :(

If I am in a clean house or in public, its not as big a deal. But I have certain germ issues that really bother me. I live with my aunt and uncle and their house is disgusting. Never vacuumed, never really sanitized, 3 cats and they all get on the counters and eat off of them, sometimes even eat the food that we set up there. My aunt puts their water dish up there for god knows what reason. Always finding cat hair in food, they let them eat off of the dishes we use. One cat pees down the kitchen sink. And me and my uncle just always get into huge arguments about it because they all think I'm being stuck up. Same goes for my brother. He is mentally challenged, but still.. he rarely showers. It is a struggle every night and if they happen to get him in, he's out in less than 5 minutes. His hands are ALWAYS dirty and he refuses to wash them. He stinks, and the worst part is, hes always touching me or hugging me!!! He always sits next to me at meals and loudly smacks his food through the whole thing with his mouth wide open the whole time. I have tried expressing how I feel to my aunt and uncle and they just get mad at me. My aunt says "just because you don't like being around him because he's the retarded kid, doesn't mean you're gonna catch anything from him. He's always gonna be your brother." It's not even like that though. I have nothing wrong with people who are disabled. I have a problem with people who don't do anything about their hygiene!!! Not only all this, but it runs a little deeper. A really long time ago, I was molested by my other brother and I have always felt uncomfortable around both of them. Anytime either one of then touches me, I jump and get instantly pissed off. How do I handle this????? Nobody in this house understands.